1. Field of the Invention
The present invention relates to the improvements of an air/fuel ratio control system of an internal combustion engine with an emission control system having at least a catalyst, and specifically to an air/fuel ratio control system capable of controlling an air/fuel mixture ratio so that the quantity of oxygen stored in the catalyst is adjusted toward a desired quantity.
2. Description of the Prior Art
In recent years, an automotive vehicle often uses a three-way catalyst to reduce oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). On automotive vehicles employing a three-way catalytic converter (a three-way catalyst) in the exhaust passage, in order to detect an air/fuel mixture ratio (often abbreviated to xe2x80x9cA/F ratioxe2x80x9d), an A/F ratio sensor, such as an O2 sensor, is usually provided in the exhaust passage upstream of the three-way catalyst. As is generally known, the purpose of the A/F sensor such as oxygen sensor is to monitor the percentage of oxygen contained within the exhaust gases at all times when the engine is running, so that the ECU can maintain the A/F ratio at as close to stoichiometric as possible. A voltage signal from the A/F ratio sensor varies depending on the air/fuel mixture ratio. In automotive vehicles with both a three-way catalyst and an A/F ratio sensor located upstream of the three-way catalyst, an electronic engine control unit (ECU) or an electronic engine control module (ECM) generally utilizes the deviation of an A/F ratio sensed by the A/F ratio sensor from a stoichiometric air/fuel ratio to arithmetically calculate or estimate the quantity of oxygen stored in the three-way catalyst. The ECU controls the A/F ratio such that the estimate (the calculated value) of the quantity of air (oxygen) stored in the catalyst is adjusted to a desired value (for example, one-half of a limit value of the quantity of oxygen stored in the three-way catalyst). When the A/F ratio is lean (excess air), air (oxygen) is adsorbed or trapped by the three-way catalyst and stored in the catalyst. Conversely, when the A/F ratio is rich (too much fuel), air (oxygen) is desorbed or released from the three-way catalyst. Generally, an oxygen desorption speed at which oxygen is desorbed from the three-way catalyst is lower than an oxygen adsorption speed at which oxygen is adsorbed by the three-way catalyst. For the reasons discussed above, the ECU increasingly compensates for the quantity of oxygen stored in the three-way catalyst, which quantity will be hereinafter referred to as an xe2x80x9coxygen storage quantityxe2x80x9d, by increasing an increment for a calculated value (or an estimate) of oxygen storage quantity, when the sensed A/F ratio is lean (excess air). To the contrary, when the sensed A/F ratio is rich (too much fuel), the ECU decreasingly compensates for the oxygen storage quantity, by decreasing a decrement for the calculated value (or the estimate) of oxygen storage quantity. Such A/F ratio control systems have been disclosed in Japanese Patent Provisional Publication Nos. 9-310635 and 6-249028.
In an automotive vehicle having an A/F ratio control system as described previously, if the actual air/fuel ratio becomes ultra lean, for example during deceleration fuel-cutoff operation, the actual oxygen storage quantity of the three-way catalyst will reach its limit value soon. However, the arithmetic-calculation section of the ECU continues arithmetic operation for the oxygen storage quantity based on the A/F sensor signal. In such a case, there is a possibility that the calculated value (or the estimate) of oxygen storage quantity is estimated or calculated as an excessive value greater than the limit value of oxygen storage quantity, even when the actual oxygen storage quantity of the three-way catalyst is kept at the limit value of oxygen storage quantity. As discussed above, there is a problem of a remarkable difference between the calculated value of oxygen storage quantity produced by the ECU and the actual oxygen storage quantity, when the A/F ratio is reduced to below an excessively lean A/F ratio less than a predetermined threshold, such as during deceleration fuel-cutoff operation. Assuming that the engine/vehicle operating condition is recovered from the previously-noted deceleration fuel-cutoff operating mode to a normal operating mode, there is a possibility of a malfunction in the A/F ratio control system owing to such an undesirably excessive rise in the calculated value of oxygen storage quantity. Also, the excessive rise in the calculated value of oxygen storage quantity may degrade the performance of the A/F ratio control. system.
Accordingly, it is an object of the invention to provide an air/fuel mixture ratio control system of an internal combustion engine which avoids the aforementioned disadvantages of the prior art.
In order to accomplish the aforementioned and other objects of the present invention, an air/fuel ratio. control system of an internal combustion engine comprises a catalyst located in an exhaust passage, for adsorbing oxygen contained within exhaust gases entering the catalyst, an air/fuel ratio sensor located in the exhaust passage upstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and entering the catalyst, and a control unit configured to be electronically connected to the air/fuel ratio sensor for controlling an air/fuel mixture ratio at as close to stoichiometric as possible, the control unit comprising an arithmetic-calculation section which calculates a quantity of oxygen stored in the catalyst on the basis of a deviation of the air/fuel ratio detected by the air/fuel ratio sensor from a stoichiometric air/fuel ratio to produce informational data indicative of a calculated value of the quantity of oxygen stored, a control section which controls the air/fuel mixture ratio so that the calculated value of the quantity of oxygen stored is adjusted to a desired value, and a limiter which prevents the calculated value of the quantity of oxygen stored from exceeding a specified level.
According to another aspect of the invention, an air/fuel ratio control system of an internal combustion engine comprises a catalyst located in an exhaust passage, for adsorbing oxygen contained within exhaust gases entering the catalyst, an air/fuel ratio sensor located in the exhaust passage upstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and entering the catalyst, and a control unit configured to be electronically connected to the air/fuel ratio sensor for controlling an air/fuel mixture ratio at as close to stoichiometric as possible, the control unit comprising an arithmetic-calculation section which calculates a quantity of oxygen stored in the catalyst on the basis of a deviation of the air/fuel ratio detected by the air/fuel ratio sensor from a stoichiometric air/fuel ratio to produce informational data indicative of a calculated value of the quantity of oxygen stored, a control section which controls an air/fuel mixture ratio so that the calculated value of the quantity of oxygen stored is adjusted to a desired value, and a limiter which prevents the calculated value of the quantity of oxygen stored from exceeding a predetermined limit value of the quantity of oxygen stored in the catalyst, the limiter comprising a determination section which determines whether the engine operates at a fuel cutoff operating mode, and an update section which, when the calculated value of the quantity of oxygen stored is above the predetermined limit value during the fuel cutoff operating mode, terminates arithmetic-operation for the quantity of oxygen stored, executed by the arithmetic-calculation section, and updates the calculated value by the predetermined limit value.
According to another aspect of the invention, an air/fuel ratio control system of an internal combustion engine comprises a catalyst located in an exhaust passage for adsorbing oxygen contained within exhaust gases entering the catalyst, an upstream air/fuel ratio sensor located in the exhaust passage upstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and entering the catalyst, a downstream air/fuel ratio sensor located in the exhaust passage downstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and leaving the catalyst, and a control unit configured to be electronically connected to the upstream and downstream air/fuel ratio sensors, for controlling an air/fuel mixture ratio at as close to stoichiometric as possible, the control unit comprising an arithmetic-calculation section which calculates a quantity of oxygen stored in the catalyst on the basis of a deviation of the air/fuel ratio detected by the upstream air/fuel ratio sensor from a stoichiometric air/fuel ratio, to produce informational data indicative of a calculated value of the quantity of oxygen stored, a control section which controls an air/fuel mixture ratio so that the calculated value of the quantity of oxygen stored is adjusted to a desired value, and a limiter which prevents the calculated value of the quantity of oxygen stored from exceeding a specified level, the limiter comprising a determination section which determines whether the air/fuel ratio detected by the downstream air/fuel ratio sensor is leaner than a predetermined lean air/fuel ratio criterion. The limiter may further comprise an update section which, when the determination section determines that the air/fuel ratio detected by the downstream air/fuel ratio sensor is leaner than the predetermined lean air/fuel ratio criterion, terminates arithmetic-operation for the quantity of oxygen stored, executed by the arithmetic-calculation section, and updates the calculated value by a predetermined limit value.
According to a further aspect of the invention, an air/fuel ratio control system of an internal combustion engine comprises a catalyst located in an exhaust passage for adsorbing oxygen contained within exhaust gases entering the catalyst, an upstream air/fuel ratio sensor located in the exhaust passage upstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and entering the catalyst, a downstream air/fuel ratio sensor located in the exhaust passage downstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and leaving the catalyst, and a control unit configured to be electronically connected to the upstream and downstream air/fuel ratio sensors for controlling an air/fuel mixture ratio at as close to stoichiometric as possible, the control unit comprising an arithmetic-calculation section which calculates a quantity of oxygen stored in the catalyst on the basis of a deviation of the air/fuel ratio detected by the upstream air/fuel ratio sensor from a stoichiometric air/fuel ratio to produce informational data indicative of a calculated value of the quantity of oxygen stored, a control section which controls an air/fuel mixture ratio so that the calculated value of the quantity of oxygen stored is adjusted to a desired value, and a limiter which prevents the calculated value of the quantity of oxygen stored from exceeding a predetermined limit value of the quantity of oxygen stored in the catalyst, the limiter comprising a determination section which determines whether the air/fuel ratio detected by the downstream air/fuel ratio sensor is a leaner air/fuel ratio than the stoichiometric air/fuel ratio, and an update section which, when the determination section determines that the air/fuel ratio detected by the downstream air/fuel ratio sensor is the leaner air/fuel ratio and the calculated value of the quantity of oxygen stored is above the predetermined limit value, terminates arithmetic-operation for the quantity of oxygen stored, executed by the arithmetic-calculation section, and updates the calculated value by the predetermined limit value.
According to another aspect of the invention, in an internal combustion engine having a catalyst located in an exhaust passage for adsorbing oxygen contained within exhaust gases entering the catalyst, and an air/fuel ratio sensor located in the exhaust passage upstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and entering the catalyst, an air/fuel ratio control system for controlling an air/fuel mixture ratio of the internal combustion engine at as close to stoichiometric as possible comprises an arithmetic-calculation means for calculating a quantity of oxygen stored in the catalyst on the basis of a deviation of the air/fuel ratio detected by the air/fuel ratio sensor from a stoichiometric air/fuel ratio to produce informational data indicative of a calculated value of the quantity of oxygen stored, a control means for controlling the air/fuel mixture ratio so that the calculated value of the quantity of oxygen stored is adjusted to a desired value, and a limiter means for preventing the calculated value of the quantity of oxygen stored from exceeding a specified level.
According to a further aspect of the invention, in an internal combustion engine having a catalyst located in an exhaust passage for adsorbing oxygen contained within exhaust gases entering the catalyst, and an air/fuel ratio sensor located in the exhaust passage upstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and entering the catalyst, an air/fuel ratio control system for controlling an air/fuel mixture ratio of the internal combustion engine at as close to stoichiometric as possible comprises an arithmetic-calculation means for calculating a quantity of oxygen stored in the catalyst on the basis of a deviation of the air/fuel ratio detected by the air/fuel ratio sensor from a stoichiometric air/fuel ratio to produce informational data indicative of a calculated value of the quantity of oxygen stored, a control means for controlling an air/fuel mixture ratio so that the calculated value of the quantity of oxygen stored is adjusted to a desired value, and a limiter means for preventing the calculated value of the quantity of oxygen stored from exceeding a predetermined limit value of the quantity of oxygen stored in the catalyst, the limiter means comprising a determination means for determining whether the engine operates at a fuel cutoff operating mode, and an update means for terminating arithmetic-operation for the quantity of oxygen stored, executed by the arithmetic-calculation means and for updating the calculated value by the predetermined limit value, when the calculated value of the quantity of oxygen stored is above the predetermined limit value during the fuel cutoff operating mode.
According to another aspect of the invention, in an internal combustion engine having a catalyst located in an exhaust passage for adsorbing oxygen contained within exhaust gases entering the catalyst, an upstream air/fuel ratio sensor located in the exhaust passage upstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and entering the catalyst, and a downstream air/fuel ratio sensor located in the exhaust passage downstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and leaving the catalyst, an air/fuel ratio control system for controlling an air/fuel mixture ratio of the internal combustion engine at as close to stoichiometric as possible, comprises an arithmetic-calculation means for calculating a quantity of oxygen stored in the catalyst on the basis of a deviation of the air/fuel ratio detected by the upstream air/fuel ratio sensor from a stoichiometric air/fuel ratio, to produce informational data indicative of a calculated value of the quantity of oxygen stored, a control means for controlling an air/fuel mixture ratio so that the calculated value of the quantity of oxygen stored is adjusted to a desired value, and a limiter means for preventing the calculated value of the quantity of oxygen stored from exceeding a specified level, the limiter comprising a determination means for determining whether the air/fuel ratio detected by the downstream air/fuel ratio sensor is leaner than a predetermined lean air/fuel ratio criterion. The limiter means may further comprise an update means for terminating arithmetic-operation for the quantity of oxygen stored, executed by the arithmetic-calculation means and for updating the calculated value by a predetermined limit value, when the determination means determines that the air/fuel ratio detected by the downstream air/fuel ratio sensor is leaner than the predetermined lean air/fuel ratio criterion.
According to a still further aspect of the invention, in an internal combustion engine having a catalyst located in an exhaust passage for adsorbing oxygen contained within exhaust gases entering the catalyst, an upstream air/fuel ratio sensor located in the exhaust passage upstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and entering the catalyst, and a downstream air/fuel ratio sensor located in the exhaust passage downstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and leaving the catalyst, an air/fuel ratio control system for controlling an air/fuel mixture ratio of the internal combustion engine at as close to stoichiometric as possible comprises an arithmetic-calculation means for calculating a quantity of oxygen stored in the catalyst on the basis of a deviation of the air/fuel ratio detected by the upstream air/fuel ratio sensor from a stoichiometric air/fuel ratio to produce informational data indicative of a calculated value of the quantity of oxygen stored, a control means for controlling an air/fuel mixture ratio so that the calculated value of the quantity of oxygen stored is adjusted to a desired value, and a limiter means for preventing the calculated value of the quantity of oxygen stored from exceeding a predetermined limit value of the quantity of oxygen stored in the catalyst, the limiter comprising a determination means for determining whether the air/fuel ratio detected by the downstream air/fuel ratio sensor is a leaner air/fuel ratio than the stoichiometric air/fuel ratio, and an update means for terminating arithmetic-operation for the quantity of oxygen stored, executed by the arithmetic-calculation means and for updating the calculated value by the predetermined limit value, when the determination section determines that the air/fuel ratio detected by the downstream air/fuel ratio sensor is the leaner air/fuel ratio and the calculated value of the quantity of oxygen stored is above the predetermined limit value.
According to another aspect of the invention, a method for controlling an air/fuel mixture ratio of an internal combustion engine, wherein the engine includes a catalyst located in an exhaust passage for adsorbing oxygen contained within exhaust gases entering the catalyst, and an air/fuel ratio sensor located in the exhaust passage upstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and entering the catalyst, the method comprises calculating a quantity of oxygen stored in the catalyst on the basis of a deviation of the air/fuel ratio detected by the air/fuel ratio sensor from a stoichiometric air/fuel ratio, to produce informational data indicative of a calculated value of the quantity of oxygen stored, controlling the air/fuel mixture ratio so that the calculated value of the quantity of oxygen stored is adjusted to a desired value, and preventing the calculated value of the quantity of oxygen stored from exceeding a specified level.
According to another aspect of the invention, a method for controlling an air/fuel mixture ratio of an internal combustion engine, wherein the engine includes a catalyst located in an exhaust passage for adsorbing oxygen contained within exhaust gases entering the catalyst, and an air/fuel ratio sensor located in the exhaust passage upstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and entering the catalyst, the method comprises calculating a quantity of oxygen stored in the catalyst on the basis of a deviation of the air/fuel ratio detected by the air/fuel ratio sensor from a stoichiometric air/fuel ratio, to produce informational data indicative of a calculated value of the quantity of oxygen stored, controlling an air/fuel mixture ratio so that the calculated value of the quantity of oxygen stored is adjusted to a desired value, determining whether the engine operates at a fuel cutoff operating mode, terminating arithmetic-operation for the quantity of oxygen stored and updating the calculated value by a predetermined limit value of the quantity of oxygen stored in the catalyst, when the calculated value of the quantity of oxygen stored is above the predetermined limit value during the fuel cutoff operating mode.
According to another aspect of the invention, a method for controlling an air/fuel mixture ratio of an internal combustion engine, wherein the engine includes a catalyst located in an exhaust passage for adsorbing oxygen contained within exhaust gases entering the catalyst, an upstream air/fuel ratio sensor located in the exhaust passage upstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and entering the catalyst, and a downstream air/fuel ratio sensor located in the exhaust passage downstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and leaving the catalyst, the method comprising calculating a quantity of oxygen stored in the catalyst on the basis of a deviation of the air/fuel ratio detected by the upstream air/fuel ratio sensor from a stoichiometric air/fuel ratio, to produce informational data indicative of a calculated value of the quantity of oxygen stored, controlling an air/fuel mixture ratio so that the calculated value of the quantity of oxygen stored is adjusted to a desired value, determining whether the air/fuel ratio detected by the downstream air/fuel ratio sensor is leaner than a predetermined lean air/fuel ratio criterion, and terminating arithmetic-operation for the quantity of oxygen stored and updating the calculated value by a predetermined limit value of the quantity of oxygen stored in the catalyst, when the air/fuel ratio detected by the downstream air/fuel ratio sensor is leaner than the predetermined lean air/fuel ratio criterion.
According to another aspect of the invention, a method for controlling an air/fuel mixture ratio of an internal combustion engine, wherein the engine includes a catalyst located in an exhaust passage for adsorbing oxygen contained within exhaust gases entering the catalyst, an upstream air/fuel ratio sensor located in the exhaust passage upstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and entering the catalyst, and a downstream air/fuel ratio sensor located in the exhaust passage downstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and leaving the catalyst, the method comprises calculating a quantity of oxygen stored in the catalyst on the basis of a deviation of the air/fuel ratio detected by the upstream air/fuel ratio sensor from a stoichiometric air/fuel ratio, to produce informational data indicative of a calculated value of the quantity of oxygen stored, controlling an air/fuel mixture ratio so that the calculated value of the quantity of oxygen stored is adjusted to a desired value, determining whether the air/fuel ratio detected by the downstream air/fuel ratio sensor is a leaner air/fuel ratio than the stoichiometric air/fuel ratio, and terminating arithmetic-operation for the quantity of oxygen stored and updating the calculated value by a predetermined limit value of the quantity of oxygen stored in the catalyst, when the air/fuel ratio detected by the downstream air/fuel ratio sensor is the leaner air/fuel ratio and the calculated value of the quantity of oxygen stored is above the predetermined limit value.